ImportError due to pybind11 autodetecting python version in CMakeLists.txt

[keckj]

Steps to reproduce:

1. Have two or more different versions of python 3 installed (python3.5 and python3.6 for example):

sudo apt-get install python3.5-dev python3.6-dev
curl https://bootstrap.pypa.io/get-pip.py -o get-pip.py
python3.5 get-pip.py
python3.6 get-pip.py

2. Install pykeops using pip (or from sources):

pip3.5 install numpy && pip3.5 install pykeops
pip3.6 install numpy && pip3.6 install pykeops

This will install two different keops modules:
<module 'pykeops' from '/usr/local/lib/python3.5/dist-packages/pykeops/init.py'>
<module 'pykeops' from '/usr/local/lib/python3.6/dist-packages/pykeops/init.py'>

3. Create python file test.py containing:

import pykeops
pykeops.clean_pykeops()          # just in case old build files are still present
pykeops.test_numpy_bindings()    # perform the compilation

4. The test script will fail for at least one python version:

• python3.5 test.py fails with ImportError: dynamic module does not define module export function (PyInit_libKeOpsnumpyb10acd1892)
• python3.6 test.py succeeds with pyKeOps with numpy bindings is working!

What really happens:

This happens because pykeops/common/compile_routines.py calls cmake on pykeops/CMakeLists.txt which contains add_subdirectory(pybind11) which will detect python3.6 by default (in this specific case). This generates a shared library <CACHE_DIR>/pykeops-1.3-cpython-35/libKeOpsnumpyb10acd1892.so targeting python 3.6 instead of 3.5 and the importlib module fails to load the library.

How to fix:

The simplest solution I found is to enforce the python version directly in the build script by using the PYBIND11_PYTHON_VERSION variable. Adding set(PYBIND11_PYTHON_VERSION 3.5) at the beginning of /usr/local/lib/python3.5/dist-packages/pykeops/CMakeLists.txt fixes the problem.

I imagine this could be done automatically by detecting python version during build / before installation. This fix could solve many issues such as #2 #8 #28 #37 and others.

[bcharlier]

Hi @Poulpy21 ,

thank you for your valuable comment and sorry for the delay!

Could you give a try on your system to see if commit fe8bc76 does the trick ? It does on my system but, just in case...

thanks again,

b.

[bcharlier]

I have included the changes in release v1.4. Fill free to reopen the issue if needed;

thanks again.

b.

[keckj]

Thanks for your patch ! I tried it by upgrading to version 1.4 directly with pip and it works like a charm :)